The present invention relates to a single reel tape cartridge in which only one reel for winding magnetic tapes is housed inside a main case.
This type of tape cartridge has a reel lock mechanism between a reel and a main case so as to prevent the reel from idly rotating during unused time. The reel lock mechanism is available in several configurations. One configuration is such that the entire reel is pressed toward a lower case by a circular-plate-shaped reel presser so that lock teeth provided between the reel presser and a lower flange are engaged with each other to prevent idle rotation of the reel (see, e.g., JP 2003-187548 A, paragraph 0016, FIG. 3). The reel presser is supported in such a way as to allow vertical movement but not to allow rotation, and is constantly depressed downward by means of a lock spring. In this example, a gin unlock tool is disposed on the inner face of a bottom wall of a boss of the lower flange, and by operating the unlock tool so as to be pushed upward by a drive shaft of a tape drive, locked engagement between the reel presser and the lower flange is cancelled and the reel is rotatably driven.
The unlock tool is formed from a component extending three arms radially to the outer circumference from a principal surface wall in the center and having downward operating nails at the top ends of the respective arms. In order to protrude each operating nail to the lower face of the case, three exit ports are provided on the bottom wall of the boss in a vertically penetrating way. Drive teeth engaging with the drive shaft are intermittently formed on the outer face of the bottom wall of the boss, and the exit ports are provided in between the teeth.
In order to enhance the molding accuracy of flange walls, the present invention aims at optimizing a flow route of resins when lower flanges are molded. Enhancing the molding accuracy by partially changing the structure of the lower flanges are known to public as disclosed in JP 2004-87067 A (paragraph 0049, FIG. 9) for example. In this example, the structure of a position reference plane formed at three locations on the lower face of a bottom wall of a boss is changed. More specifically, the position reference plane originally having a solid structure is changed into a C-shaped frame so as to prevent “surface sink” during molding. It is to be noted that a reel lock mechanism in this example prevents idle rotation of the reel during unused time by engaging lock teeth formed on the periphery of a lower flange with a reel lock. Consequently, the exit ports for operating nails essential for the former example are not formed on the bottom wall of the boss in this example.
When the exit ports are formed on the bottom wall of the boss across the circumferential direction as described before, melted resin flows while de-touring the exit ports during molding process of the lower flange. Consequently, when the melted resin which detoured the exit ports converge, weld lines are generated, which causes uneven filling of resin and creates distortion on flange walls. More specifically, when a gate position is set in the center on the lower face of the low flange, a resin flow to a flange wall on an extension of an exit port tends to delay in proportion to the resin flow to other sections. This causes dispersion in filing density of resin on the flange wall in circumferential direction, generating waviness and inclination on the flange wall after solidification. The run-out amount on the flange face caused by the waviness and the inclination amounts to maximum 0.292 mm, which has been a major hurdle of achieving high-density and high-speed read/write access to magnetic tapes.